Pressure transducers are used to measure pressure in environments of interest, such as media-filled chambers used in the extrusion of plastics, injection molding processes, down-hole sensing in oil and gas exploration, combustion engines, and various other applications.
Pressure transducers conventionally comprise a diaphragm at one end that can be brought into contact with process media in the environment of interest and displaced by the pressure of the process media. For example, in the case of a pipe, the pressure transducer may be inserted (or screwed) into an opening in the wall of the pipe, such that the diaphragm is in contact with the media (e.g., molten plastic, fluid, etc.) inside the pipe.
The diaphragm of the pressure transducer is mechanically coupled to a sensor element, which is disposed inside a housing. The sensor element measures the pressure of the process media in the environment of interest, based on a physical parameter such as compression, displacement or deformation of the sensor element, with the media pressure being transferred to the sensor element from the diaphragm either directly or through a mechanical coupling. The sensor element may comprise, for example, piezoelectric or piezoresistive crystals configured to provide an electrical signal indicative of the sensed pressure.
In a conventional pressure transducer, the sensor element is held in place (against deflections of the diaphragm) by a support (also referred to as a pedestal), which in turn abuts, and is held in place by, an inner surface of the transducer housing.
The sensor element of a pressure transducer is typically sensitive to small changes in the physical parameter that it uses to measure pressure. For example, where pressure is measured based on the compression of the sensor element, a small compressive load on the sensor element may be significant to the pressure measurement. Accordingly, imperfect construction or misalignment of the components of the pressure transducer during manufacture or assembly can lead to inaccurate pressure readings if an uneven or undesired load is exerted on the sensor element as a result.
Another consideration in pressure transducer design, particularly for high-temperature applications, relates to thermal expansion of the pressure transducer components. The housing of the pressure transducer is typically constructed from stainless steel, which has a relatively high coefficient of thermal expansion. The sensor element and the support, however, are often made from other materials, such as ceramics, that have lower coefficients of thermal expansion. This imbalance in thermal expansion properties can lead to uneven expansion of the internal and external components of the pressure transducer, especially at higher temperatures, which, if not compensated for, can have an undesired impact on the loading of the sensor element and cause inaccurate measurement of the pressure in the environment of interest.